Mega-piranha had teeth a T. Rex would have envied

An ancient relative of piranhas weighing about 20 pounds delivered a bite with a force more fierce than prehistoric whales. The ancestor of the modern piranha had a bite-force that dwarfed that of prehistoric whale-eating sharks, the four-ton ocean-dwelling Dunkleosteusterrelliand – even – Tyrannosaurus rex. Besides the force of the bite, Megapiranhaparanensis appears to have had teeth capable of shearing through soft tissue in the same way today’s piranhas do. Modern black piranhas, which average 2.5 pounds in weight, can deliver a bite with a force 30 times its body weight. Their ancient ancestors were able to pierce thick shells and crack armoring and bones.

According to a report from the University of Washington, student researcher Stephanie Crofts said “If our calculations are correct, Megapiranha was probably a bone-crushing predator taking bites of anything and everything,” she said. Crofts is co-author of “Mega-Bites: Extreme jaw forces of living and extinct piranhas.” Crofts, who is pursuing a doctorate in biology, published her report on the fish antediluvian beast in the online journal Scientific Reports.

Megapiranha, which lived 10 million years ago, had a bite-force was extrapolated from the first field measurements of the biting force of largest piranha living today. A speciemen of Serrasalmusrhombeus or black piranha, weighing 2.5 pounds can deliver a bite-force of 320 newtons, or about 72 pounds or 30 times its body weight. The force is nearly three times greater than the bite force of an equivalent size American alligator.

Based on the 2 ½ pound piranha and other specimens tested in the wild, Megapiranhaparanensis, which weighed approximately 22 pounds, could have had a bite force anywhere from 1,240 to 4,750 newtons – or 280 to 1,070 pounds – and possibly more. Previous estimates for the T. rex estimated its bite-force at 13,400 newtons, or 3,000 pounds of force, but that’s nowhere near slamming shut its maws at 30 times its body weight.

Pound for pound, Megapiranha and black piranha have the most powerful bites among carnivorous fishes, living or extinct. According to Crofts' paper, “For its relatively diminutive size, Megapiranhaparanensis’ bite dwarfs other extinct mega-predators” including the enormous whale-eating Carcharodonmegalodonand the monstrous Dunkleosteusterrelli, a four-ton armored fish.

“We were surprised that in spite of their long history and infamous reputations that no one had ever measured their bite forces,” said Justin Grubich, with the American University in Cairo, Egypt, and lead author of the paper. “When we finally started to get the data, we were blown away at how tremendously strong the bites were for these relatively little fish.”

As the paper says, “While anecdotes of piranha-infested waters skeletonizing hapless victims are generally hyperbole, the effectiveness of their bite is not.”

Just how does one measure the bite force of a piranha living in the wild? Well, you get out your rod and reel and go fishing. Land a specimen, then hang tight to the tail with one hand and use your other hand to support its belly while offering the fish a chance to bite the plates of a customized force gauge. “Piranhas are ornery little fish so they bit down as hard as they could,” Crofts said. The black piranha’s bite is so powerful in part because of its massive jaw muscles and rope-like tendons that together account for 2 percent of the fish’s overall weight, the scientists found. Further the shape of their jaw has evolved into a powerful lever, “one of the highest jaw-closing mechanical advantages ever identified in fishes,” the paper said.

Crofts’ main contribution involved analysis of how Megapiranha teeth handled stresses and how breakable the teeth might have been. The scientists were particularly interested because Megapiranha’s unusual teeth appear to do two things at the same time, one the piranha-like ability to shear soft tissues and the other an ability to bite like the nut-crushing pacu, piranha’s close relative.

Based on a fossilized jaw and three teeth, Crofts conducted a computer generated “finite element analysis” for the team. “We found the Megapiranha teeth had the same maximum strength like you saw in regular piranha, but then the patterns of stress distribution within the tooth was also similar to fish able to eat hard-prey,” she said.

The actual diet remains a mystery, but during the time when Megapiranha lived a lot of potential prey species were gigantic. “Thus it is reasonable to assume the food resources available to Megapiranha would likely have required jaw forces and dental weaponry capable of capturing and processing very large prey,” the paper says.